Electric furnace smelting of copper concentrates



Nov. 7, 1967 c. ARENTZEN ETAL 3,351,452

'ELECTRIC FURNACE SMELTING OF COPPER CONCENTRATES Original Filed June30, 1961 COPPER CONCENTRATES REACTOR, FIRsTsTACE AIR l [sandsoz RECOVERYl I [REACTOR,SECONO sTACEI I HOT CASES I CALGINE CONTAINING Sand S02 f LA v [FIRST ELECTRIC sMELTINC FuRNAcI I I I I COPPER I I-uRNACE CAsEs AGOONTAININC SO2 ELECTROLYTIC REFINING CATHOOE COPPER ANOOE MUD I COKEFIRE REFININC FURNACE I l Au,Ag,Se,Te, eIc. RECOVERY CAST COPPERCOMMERCIAL sI-IAPES |SECONOELECTRIC FURNACI I I I I I I I I I I I I I II I I I N-C PPER ROLLgY NOZS, COO, etc.

Y @IRO ELECTRIC FURNACI EIARREN SLAC SLAC PRODUCTS CHARLES ARENTZENTHEODORE G. FUILMOR FRANCIS L HOLDERREED United States Patent 3,351,462ELECTRIC FURNACE SMELTlNG GF CPPER CONCENTRATES Charles Arentzen,Theodore G. Fulmor, and Francis L.

Holderreed, Anaconda, Mont., assignors to The Anaconda Company, NewYork, NX., a corporation of Montana Continuation of application Ser. No.121,251, June 30, 1961. This application Jan. 29, 1965, Ser. No. 430,247

This application is a continuation of application Ser. No. 121,251, ledlune 30, 1961, now abandoned.

This invention relates to smelting of copper concentrates and moreparticularly to a process of direct smelting of roasted copperconcentrates to blister copper, preferably utilizing electric furnacesmelting techniques.

Known copper ore deposits are, for the most part, composed of coppersulfides mixed With iron sulfides, Present extraction processes involvefirst crushing the ore to fine size, thereby liberating thecopper-bearing minerals of the ore from the gangue. The copper sulfideof the crushed ore is next concentrated in a flotation operation inwhich the dotation reagent is one which will float the copper sulfide.The flotation concentrates, or copper concentrates, which in addition tocopper sulfide contain certain other components of the ore, mainlysilica and iron sulfides, are dried and roasted in a roasting furnace tooxidize the iron sulfide and to eliminate a considerable portion of thevolatile materials. The product of the roasting `operation, known ascalcine, is a dry, finely-divided solid composed chiefly of coppersulfide7 iron sulfide, some iron oxide, and the gangue originallypresent in the concentrate- The calcine is smelted with silica and lime(a slagforming base) in a reverberatory furnace to produce matte andslag. The matte is composed essentially of copper sulfide and ironsulfide. The slag contains the other constitutents of the charge, mainlyiron oxide and silica. Since the molten matte is not miscible with themolten slag, the matte and the slag readily separate in two distinctlayers or phases, the slag floating on top of the matte. The slag isdrawn off and discarded, The matte, to which some silica has been addedis treated further in a converter by blowing air through it to oxidizethe iron sulfide and to reduce the copper sulfide to metallic copper.More specifically, the air first changes the iron sulfide to iron oxidewhich combines with the silica to form a slag. After pouring off thisslag, continued blowing results in changing part of the copper sulfideto copper oxide which reacts with the remaining copper sulfide toproduce metallic copper. This metallic copper, known, when cast, asblister copper, is of approximately 99% purity` Should a copper ofgreater purity be desired, the blister copper is further refined in anelectrolytic refining cell. The product of electrolytic refining, knownas cathode copper, is virtually 100% pure, the main impurity beingsulfur from the sulfate electrolyte. To eliminate this sulfur and minorother impurities and to prepare the copper for casting into commerciallyacceptable shapes, it is fire refined in a reverberator-type furnace. Atthe conclusion of the fire refining operation, the copper contains about0.03 to 0.05% oxygen, the only impurity present to any appreciableextent. Blister copper may also be fire refined to remove impuritiesprior to the electrolytic refining, or in some cases instead ofelectrolytic refining.

The present invention contemplates a process whereby blister copper maybe produced by direct smelting of properly roasted copper concentrates,or calcine, thereby eliminating the reverberatory furnace and convertorsteps in the production of copper, as outlined above,

According to the process of the present invention, the copperconcentrates are oxidized in a suitable roasting Ficel furnace so thatsubstantially all the iron sulfide is converted to iron oxide and themajor part of the copper sulfide, preferably about two-thirds of thecopper content, is converted to copper oxide. This is relatively easy t0accomplish with the close control made possible by utilizingfluidized-bed roasting techniques, since copper sulfide will not odidizeso long as any iron sulfide remains unoxidized.

When essentially all the iron sulfide has been ccnverted to iron oxideand the desired molecular proportion lof copper oxide to copper sulfidehas been attained, the roasted product, or calcine, is charged into anelectric furnace, with added fluxes if desired although such are notessential. As the charge is brought up to smelting temperature, thecopper sulfide and copper oxide react to produce metallic copper,

This reaction determines the proper molecular proportions of copperoxide to copper sulfide. Preferably, the concentrates are roasted tooxidize somewhat more than two-thirds of the copper to cuprous oxide,and then a sufficient amount of extraneous sulfur-bearing material suchas copper concentrate is added to establish the molecular ratio ofcopper to sulfur at about 6:1.

The iron oxide will form a slag on top of the molten copper and may beeasily drawn off. The concentrates generally contain at least theminimum -requisite `amount of silica and other slag-forming agents toslag the iron oxide. Hence in general no fluxes are required for thisstep; but added silica and other slag forming agents may facilitateformation of the iron oxide slag and result in a better separation ofthe slag and metallic copper. An electric furnace is preferred forcarrying out the smelting operation because of the close control oftemperature it provides. The slag may be treated to extract the iron itcontains. The metallic copper, or blister copper, produced may berefined in an electrolytic refining cell and then lire refined in aconventional manner, as outlined above, if cathode copper is desired.Again, the blister copper may be fire refined prior to the electr-olytierefining to remove impurities.

The accompanying flow sheet illustrates a specific adaptation of thepresent invention. Referring to it, copper concentrates are roasted in atwo stage fluid-bed reactor. (Although two reaction stages are ingeneral preferred because thereby maximum elimination of arsenic withminimum formation of magnetite may be achieved, it is entirely feasibleto carry out the process in a single stage reactor.) The copperconcentrates supplied to the first stage of the reactor are the typicalraw copper concentrates from the flotation cell; that is, they are amixture essentially of copper sulfide, iron sulfide, siliceous gangue,and volatile materials such as labile sulfur. The concentrates may havebeen thickened to some extent by the normal drying action incident tothe passage of time or by artificial partial drying.

In the first stage of the reactor, the concentrates are dried andpartially roasted by heating with the hot gases from the second stage ofthe reactor to produce a dry, solid, partially roasted concentrate.Sulfur and sulfur dioxide may be recovered from the gases from thisstage in a recovery operation. A minimum amount of oxygen admitted tothe first stage will favor formation of arsenous rather than the morediflicultly volatilized arsenic oxide if the concentrates containarsenic, The dry partially roasted concentrates are transferred to thesecond stage of the reactor, which may be in the lower part of the samevessel, the first part of the reactor being in the upper part. In thesecond stage, air, which may be preheated, is introduced and blownthrough the concentrates. All remaining labile sulfur is distilled offand substantially all of the remaining sulfur of the iron sulfide isoxidized to sulfur dioxide with the formation of iron oxide. Inaddition, part of the copper sulfide is oxidized to copper may be addedto the calcine to attain the proper copper t0 sulfur ratio. Thetemperature of the electric furnace is raised to approximately 1500D C,which is sufficiently high to smelt the charge. This causes the copperoxide oxide.' Some excess `of air may be supplied to this stage t0 5 andcopper sulfide to react as indicated above, producing assure adequateoxidation of the iron and copper sulfide metallic copper of the purityof blister copper, and sulfur and to minimize magnetite formation. Thecopper condioxide. The sulfur present in the copper concentrates orcentrates will be raised from ambient temperature to the othersulfur-bearing material added to the furnace charge maximum practicabletemperature consistent with the also reacts with copper oxide to producemetallic copper character o'f the concentrates and loptimum performance10 and sulfur dioxide. of the roaster to reduce power consumption in thesub- The iron oxide present in the electric furnace charge sequentelectric furnace smelting step. The time it Will take forms a slag withthe silica present and fioats on top Kof the for the copper concentrateto pass through the reactor metallic copper. Although, as indicatedabove, the con- Will vary with the amount and nature of the particularcentrates normally contain sufiicient silica to `form a slag componentsof the charge. The output of the reactor is 15 with all the ironpresent, additional silica, lime, and other calcine, a dry,finely-divided solid composed chiefiy of slag-forming agent may be addedto the furnace charge copper oxide, copper sulfide, iron oxide, a silicaand other when desired to improve the quality of the slag and thenon-volatile components of the gangue originally present ease ofseparating it from the copper, in the concentrate. The metallic copperproduct of the electric furnace When essentially all of the iron sulfiedhas been oxidized 20 may be electrolytically refined in a conventionalelecand at least a part, preferably two-thirds by molecular trolyticcell, yielding cathode copper and anode mud. The Weight, of the coppersulfide has been oxidized to copper cathode copper may be subjected tofire refining in a conoxide the resulting calcine is charged to a firstelectric ventional manner to produce a cast copper in commersmeltingfurnace. As set forth previously, the proper cial shapes and a slightamount of slag. Gold, silver, molecular Weight ration 2:1 for cuprousoxide to cuprous 25 selenium, tellurium and `other valuable byproductsmay sulfide is determined by the reaction that .occurs in electric berecovered from the anode mud. The copper may, if srnelting furnace,desired, be fire refined before being electrolytically `refined toremove some of its impurities. 2Cu2o+cu2s6cu+soz The slag produced inthe first electric smelting furnace In order to assure the proper ratioof copper Oxide t0 30 is rich in iron oxide and thus in iron; and sinceit usually COPPCT Sulde, the roasting adVafltageOUSly is carried t0 isimpossible to effect substantially complete separation a Point Slightlybeyond the PFOPeI' ratio; that is, the C011- of copper from it, itscopper content is appreciable. It centrates are roasted until somewhatmore than the proper may be treated with a reducing agent Such as cokein a amount of copper sulde has been converted to copper second electricfurnace to yield an iron-copper alloy rich OXide- Then, in Order t0adjust the Proportion 0f COPPe 35 in iron, and a barren slag; or it maybe subjected to step- Oxide t0 COpper sulfide t0 the PrODCr TRO, 'duHITIOUH Wide reduction to make first a copper-rich iron alloy and Of raWCOpper concentrates is added to the calcine then a low-copper iron alloyand a barren slag. The barcharged to the electric furnace in order tobring the ren slag may be utilized for making slag products suchmolecular raO 0f COPPCT t0 Sulfur II the Charge Subas buildingmaterials, aggregates, insulation, etc. The ironstantially to the propervalue of 6:1. In place of or in 40 copper alloy may be treated withsodium sulfide and lime .addition to the raw copper concentrates,pyrites or other in a third electric furnace to yield substantiallycopper- 'suitable sulfidic material (including even free sulfur) freeiron andacupriferous slag.

Weight and Analysis Charge Wt., Pounds Test' Metal Phase Slag PhaseCalcine Silica CaO Coke Cone. Wt., lbs. Percent Percent Percent Wt.,lbs.Percent Flour Cu Fe S Cu 15.05 3. 88 0 0. 74 96. 22 0. 05 o 15. 95 18. 710.0 2. 55 o. 5 0 o 0. 98 98. 08 0.05 o 10. 79 19. 5 15 1.19 o 0 1.5 g422:26 gg 18:26 11. 36 5.2 15.0 1. 2 0 0 1. 3 3. 49 98. 28 0.04 0.11 10.91 6. 4 15. 0 0 0 0 1. 5 3.83 98. 01 0. 19 o. 29 10. 02 7. 1 15.0 0 00.75` 1.5 4.41 92.45 4.o 0.59 s. 18 2.8

Slag

7-{S5111132 I 973 126 M8 123 820 S9 165 Percent Distribution Analysis,Slag Percent Accounting Phase (cont.) Test Metal Phase Slag PhasePercent Percent Cu S Fe Cu S Fe Cu S Fe Fe S 31. 7 0. 05 19. 2 0 80. 8199 -100 88. 2 2. 91 10s. 5 29. 7 0. 07 30. 2 0 0.02 69. 8 109 99.98108. 0 3. 41 98 45.3 0.14 g: 13.1 9.0 99.0 99.5 19.18 97.5 44. 4 o. o582. 3 44. 5 0. 03 16.9 55, 5 99.97 91. 7 1. o7 91. 8 49. 7 o. 03 s4. 177. 0 0. 14 15. 9 23. 0 99. 86 98. 2 1. 42 93. 4 6 53.7 3.0 94.3 9.9 3.65.7 90.1 96.4 95.1 27.8 92.0 Pff?, l: 3. 0 92. 8 63 7. 2 37 97. 5 9e. 8

* White Metal. (a) Performed in two stages, white metal phase producedin addition to slag and Cu.

The slags produce by the iire refining process and by the third electricfurnace will contain a substantial amount of copper and may be recycledto the first electric smelting furnace as indicated by the broken lines,so as to extract the maximum amount of copper possible. Sulfur andsulfur dioxide may be recovered from the gases leaving the reactor andthe first electric furnace respectively in a recovery operation.

Since a minimum of flue gases are produced by the process hereindescribed, a simplified flue system may be provided. Plant cleanlinessas well as operating and working conditions thereby are materiallyimproved.

Above are specific examples of the process described as carried out inan electric furnace. The calcine and copper concentrates charged to theelectric furnace assayed as follows:

iron in the metal phase resulted. However, a high metal phase weight anda high percentage distribution of the copper in the metal phase wasproduced. The slag from Test 6 contained metallic iron as well asmagnetite, pyrrhotite and glass. The metal phase in Test 6 containedsome chalcocite and silicates, with no iron minerals other than thesilicates being present.

Test 7 indicates the results to be expected of smelling the slag fromthe primary electric furnace in the second electric furnace. In thistest some of the slag from Test 5 and some of the slag from Test 6 wereused. The slag from Test 7 was free of magnetite but had dispersed in ita. small amount of copper and some sulfides, fayalite, iron-rich glass,and some metallic iron alloy. The metal phase of Test 7 containedmetallic iron and copper, a

Cabine; Cu7 23,0%; S, 22%; S043, 1.3%; Fe, 32,7%; low-content coppersulfide, a high iron-content copper sul Feaoi, 16.7%; Si02, 9.6%.`Concentrates; Cu, 23.2%; de, andasmallamountof slag. S, 39.1%; Fe,29.0%; Fe304, 1.2%; SiO2, 3.0%. Two additional tests gave the followingresults:

Calcine Charge Metal Produced Test Percent Cu S Fe FeaOi Wt. Wt. (lbs.)Percent Cu S Fe FeaOi SOiS Percent Percen Percent Percent PercentPercent Percent Percent Dist. Dist. ist. ist.

Slag Produced Accounting, Percent Dust Loss, Kw.hr. per Test Cu S FeFeaOi Percent 'lonCalcine Wt. Percent Cu S Fe FeaOi Per- Percent Per-Percent Per- Percent Per- Percent cent Dist. cent Dist. cent ist centDist.

The charge to the furnace was mixed and then fed in increments,interrupting the power to make the additions of charge. Each teststarted with a. cold furnace and a cold charge. After all the charge wasmelted, power was maintained to raise the bath temperature, insuringproper separation of the furnace products. The results were as shown inthe table in column 4 preceding.

This tabulation sets forth the weight in pounds of the .constituents ofthe charge to the electric furnace. It also sets forth an analysis byweight and by distribution of the constitutents of the metal and theslag. The high copper content of the slag was due to the limited scaleof the test and a limited control over the power supplied to theelectric furnace. Test results indicate that no added uxes are requiredto produce copper directly. A great deal of metallic copper was found inthe slag from Tests l and 2, indicating that the reduction was completebut that the slag was too viscous to permit separation of the copper.

In Tests 3 to 6 the sulfide content of the calcine was `adjusted byadding raw copper concentrates. This resulted in improved copperproduction. The slags from Tests 3, 4, and 5 physically resembled commonreverberatory furnace slags, with magnetite, fayalite and glass beingpresent. In these tests precipitation of magnetite on copper globulesmay have occurred and prevented a better separation of copper from theslag. The white metal phase formed in Test 3 was principally chalcocitewith some metallic copper andeilver minerals. Using only acalcineconcentrate charge, as in Test 5, resulted in a high percentageby weight of copper in the metal phase, a good ratio of metal weight toslag weight, and a high percentage of the copper accounted for.

When coke is added to the calcine-concentrate charge, as in Test 6, alower percentage by weight of copper to The above tabulation of theseadditional tests sets forth the weight in pounds of the constituents ofthe calcine charged to the electric furnace, the percentage of theconstituents of the metal and slag by weight and by distribution, anaccounting for the separate constituents, the dust lost, and an estimateof the kilowatbhours required to smelt a ton of calcine. In previousTests 3 to 6 the sulfide content of the calcine was adjusted by addingraw copper concentrates. In Test 8 the calcine was of a higher sulfurcontent than in Tests l to 7, and no concentrates were added to malte upthe furnace charge. In Test 9, calcine which had been produced in amultiple hearth roaster with all the copper and some of the iron stillin the form of sulfide was smelted with the production of white metal(matte).

The copper assay of the slag produced was the same in both tests. InTest 9 the percentage of copperrecovered in the metal phase (matte inthis case) was greater than in Test 8, probably because a smaller amountof slag was produced. Dust losses from both tests are of the samemagnitude. The difference in weights of charge used in Tests 8 and 9 maypartially account for the wide spread in power consumption. Test 9 wasperformed with a con ventional matte grade calcine to smelt in acomparison with Test 8 forv which the calcine had been roasted to`convert about two-thirds of the copper to copper oxide.l

These tests show that even a matte grade calcine can be effectivelysmelted in an electric furnace, but the metal phase (matte) will have tobe treated to eliminate the In the appended claims where the reaction ofsulfur is referred to it is understood that the sulfur may be either ina free state or combined as a sulfide.

Various changes may be made in the details of the process hereindescribed without departing from the invention for sacrificing any ofthe advantages thereof, the scope of the invention being set forth inthe appended claims.

We claim:

1. A process for producing metallic copper from copper concentratescontaining iron sulfide and copper sulfide which comprises roasting thecopper concentrate in the presence of oxygen at a sufficiently hightemperature to convert substantially all the iron sulfide to iron oxideand at least a part of the copper sulfide to copper oxide, and smeltingthe roasted concentrate directly in an electric furnace in the presenceof slag forming agents and an amount of sulfur corresponding inmolecular proportion to about one-sixth' of the amount of copper presentat a temperature sufficiently high to cause the sulfur to react with thecopper oxide to reduce the copper oxide to metallic copper and to causethe iron oxide to form a molten slag with the slag-forming agents.

2. A process for producing metallic copper as set forth in claim 1, inwhich the slag and metallic copper are separately Withdrawn from thefurnace and the copper is subjected to a refining operation to producehigh purity commercial copper.

3. A process for producing metallic copper from copper concentratescontaining iron sulfide and cuprous sulfide which comprises roasting thecopper concentrate in the presence of oxygen at a sufficiently hightemperature and for such length of time as to convert substantially allof the iron sulfide to iron oxide and about onethird of the coppersulfide content thereof to cuprous oxide, and directly smelting theroasted concentrate in the presence of slag-forming agents at atemperature sufficiently high to form a slag from the iron oxide and theslag-forming agents and to cause the copper oxide to react with thecopper sulfide to produce metallic copper.

4. A process for producing metallic copper as set forth in claim 3 inwhich slag and metallic copper are separately withdrawn from thesmelting operation and the slag is treated for the recovery of byproductvalues.

5. A process as set forth in claim 4 in which the slag is smelted with areducing agent for the production of metallic iron.

6. A process as set forth in claim 4 in which the slag containing ironand copper is smelted with a reducing agent to form a metal phase and abarren slag, the metal phase is heated in the presence of an additionalslagforming agent to produce metallic iron substantially free of copperand a copper-bearing slag, and the metallic iron is separated from thecopper-bearing slag.

7. A process as set forth in claim 6 in which the reducing agent is cokeand in which the additional slag-forming agent comprises sodium sulfideand lime.

8. A process as set forth in claim 6 in which the copperbearing slag ischarged with fresh roasted copper concentrates into the electricsmelting furnace.

9. A process for producing metallic copper from copper concentratescontaining copper sulfide and iron sulfide which comprises roasting thecopper concentrates in the presence of oxygen `at a sufficiently hightemperature to convert somewhat more than two-thirds by molecularproportion of the copper sulfide to copper oxide and to convertsubstantially all of the iron sulfide to iron oxide, charging theroasted concentrates directly into a smelting furnace together withsufficient extraneous sulfurbearing material to establish a molecularratio of copper to sulfur in the change corresponding substantially to6:1, and smelting such charge in the presence of slag-forming agents ata temperature sufficiently high to form a slag of the iron oxide andslag-forming agents and to cause the copper oxide to react with thecopper sulfide and added sulfur to reduce substantially all the copperoxide and copper sulfide to metallic copper.

10. A process for producing metallic copper as set forth in claim 9 inwhich the extraneous sulfur-bearing material is copper concentrates.

11. A process for producing metallic copper Ias set forth in claim 9 iswhich the slag and metallic copper are separately withdrawn from thefurnace, and the copper is subjected to a refining operation to producehigh purity commercial copper.

12. A process for producing metallic copper as set forth in claim 9which includes subjecting the metallic copper to fire refining in thepresence of a slag-forming agent to produce refined copper and arefining slag, separating the refined copper from the refining slag, andcharging the refining slag together with roasted copper concentratesinto the smelting furnace.

13. A process for producing metallic copper from copper concentratescontaining copper sulfide which comprises roasting the copperconcentrates in the presence of oxygen at a sufiiciently hightemperature and for such length of time as to convert over two-thirds ofthe copper sulfide content thereof to copper oxide, adding sulfurbearingmaterial to the roasted copper concentrates in an amount sufficient toestablish a molecular ratio of copper to sulfur in the resulting mixtureof substantially 6:1, and smelting such mixture at a temperaturesufliciently high to cause the suldic constituents of both the unroastedcopper concentrate and of the roasted copper concentrate to react withthe copper oxide of the roasted copper concentrate to produce metalliccopper.

14. A process according to claim 13 in which the sulfur-bearing materialis copper concentrates.

References Cited UNITED STATES PATENTS 153,573 7/1874 Kidwell 75--21820,134 5/ 1906 Riveroll 75--65 900,346 10/1908 Benjamin 75-74 X1,238,279 8/1917 Dwight 75-74 X 1,811,920 6/1931 Dickson 75-7 1,873,8008/1932 Wejnarth 75--10 1,976,735 10/1934 Kuzell 75-21 2,194,454 3/ 1940Greenwalt 75-74 2,210,479 8/1940 Booton 75-7 2,261,946 11/1941 Avery75-21 X 2,438,911 4/ 1948 Gronningsaeter 75--24 2,653,868 9/1953 Lichty75-24 FOREIGN PATENTS 650,048 2/ 1951 Great Britain.

OTHER REFERENCES Butts: Copper, The Metal and Its Alloys and Compounds,Reinhold Publishing Corp., New York, 1954, pages 84-118.

Newton et al.: Metallurgy of Copper, John Wiley and Sons, Inc., NewYork, 1942, pages 35-16l.

DAVID L. RECK, Primary Examiner.

P. WEINSTEIN, Assistant Examiner.

UNITED STATES PATENT OFFICE CERTIFICATE 0F CORRECTION Patent No.3,351,462 November 7, 1967 Charles Arentzen et al.

It is hereby certified that error appears in the above numbered patentrequiring correction and that the said Letters Patent should read ascorrected below.

Column Z, line 7, for "odidize" read oxidize Column 3, line 25, for"ration" read ratio column 4, line 35, for "wide" read wise columns 3and 4, in the table, under "Weight and Analysis, Slag Phase, Wt., 1bs.",line 6 thereof, for "8.18" read 8.81 same table, under "Analysis, SlagPhase (cont.) Percent Fe", line 7 thereof, for "3.0" read 33.0 sametable, under "Percent Distribution, Metal Phase, Cu", line 5 thereof,for "82.3" read 83.1 Column 8, line 3, for "change" read charge Signedand sealed this 21st day of January 1969.

(SEAL) Attest:

EDWARD J. BRENNER Commissioner of Patents Edward M. Fletcher, Jr.

Attesting Officer

1. A PROCESS FOR PRODUCING METALLIC COPPER FROM COPPER CONCENTRATESCONTAINING IRON SULFIDE AND COPPER SULFIDE WHICH COMPRISES ROASTING THECOPPER CONCENTRATE IN THE PRESENCE OF OXYGEN AT A SUFFICIENTLY HIGHTEMPERATURE TO CONVERT SUBSTANTIALLY ALL THE IRON SULFIDE TO IRON OXIDEAND AT LEAST A PART OF THE COPPER SULFIDE TO COPPER OXIDE, AND SMELTINGTHE ROASTED CONCENTRATE DIRECTLY IN AN ELECTRIC FURNACE IN THE PRESENCEOF SLAG FORMING AGENTS AND AN AMOUNT OF SULFUR CORRESPONDING INMOLECULAR PROPORTION TO ABOUT ONE-SIXTH OF THE AMOUNT OF COPPER PRESENTAT A TEMPERATURE SUFFICIENTLY HIGH TO CAUSE THE SULFUR TO REACT WITH THECOPPER OXIDE TO REDUCE THE COPPER OXIDE TO METALLIC COPPER AND TO CAUSETHE IRON OXIDE TO FORM A MOLTEN SLAG WITH THE SLAG-FORMING AGENTS.